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Gas radiant heat furance making thumping noise

Our radiant gas heat furnance is making a thumping noise when it is running. I have bled the lines including the overflow release valve on the top of the furnance and 2 valves near the ceiling. There is another valve on the side of the furance near the bottom which I have not bled due to it being stripped. The question is should I attempt to open this valve and bleed this line also and would this solve the problem?

Re: Gas radiant heat furance making thumping noise

You have a boiler there from your description of the heating system.

Almost impossible to tell the cause of the "thumping" from your post & description.

You seem to be concentrating on bleeding the system piping, which is usually not the cause of thumping, unless you're absolutely sure the sound is coming from that location.

Since a common cause of this noise is defective fuel pumps or gas valves, it sounds like it would be best if you have a tech look at it right away.

If it's an oil system, a defective oil cutoff valve or leaking seal in the oil burner pump or defective oil nozzle could be causing too much oil to enter the combustion chamber, then ignite, causing the thump & sometimes a "puffback", sometimes with soot entering the boiler room.

Similar problems can cause a similar condition with gas-fired equipment.

Re: Gas radiant heat furance making thumping noise

JacktheShack Thanks for your response on the heating problem. Had heating expert take a look and listen. Ends up it is the lime deposits cooking internally. No danger besides the thumping which may get worse. Hope to make it until spring and do a new furnance.
Thanks again, Frontlinetom

Re: Gas radiant heat furance making thumping noise


Thanks for posting back.

Sorry I missed the part about the unit being gas-fired--you DID mention this in your header.

I also should have connected "thumping" with possible lime deposits.

Unless the boiler is real old, there's no need to replace it.

Lime deposits can often be successfully removed by chemical treatment of the boiler water.

There's a product called Lime Dissolver by Comstar for $15/gallon that is added to the boiler water for a day or 2, then flushed from the system.

It's a common problem for boiler owners who have hard water in their area.

Other scale & lime treatments are 8-Way by Rector Seal for $10/qt. and Stewart Hall's Scalomatic for $40/gallon.

These chemicals are nasty so it's usually best to let a pro do the flush.

If your present boiler person is unfamiliar with the procedure, the countermen at some of the local plumbing supply houses in your area may be able to recommend someone.

Re: Gas radiant heat furance making thumping noise

Jack, Thanks again for the additional info. I also should have mentioned that the unit is 30+ years old so some deposits are due to collect in there. Will suffer with the noise until spring and see what a new one costs and/or do your suggested procedure. Does your flush procedure go through the whole house system (radiant heat) or can just the boiler itself be flushed?

Re: Gas radiant heat furance making thumping noise

IIRC it has to be allowed to circulate thru the system to be effective.

According to my product catalogs, the chemicals are designed not to harm any components in the heating system.

Re: Gas radiant heat furance making thumping noise

Jack the shack, All of sudden the thumping noise is gone. Had a couple of days with the heat up to 76 degrees.( Not sure if the tech fooled with it) Re-adjusted the thermostat down to 70 degrees and so far no noise what-so-ever. Maybe cooking those deposits broke them down to where they are now circulating through the system.
It's been quiet for about a week now.

But,I will check out getting some lime treatment to do a flush in the near future.

Again, Thanks for your help.


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